Ch 19: Air Quality

While the Clean Air Act has controlled pollutant emissions
from all air pollution sources, the greatest success can be found in the
control of on-road mobile sources. Emissions reductions from motor
vehicles have accounted for 84 percent of the total emissions reductions
of the six criteria pollutants since 1970.

Air pollutant levels nationally have improved considerably, and although some areas have shown increases, concentration levels in most urban areas, where problems have historically been the most severe, have shown marked
improvement in response to stringent controls.

Percent
Decrease in Concentration of Criteria Pollutants [1]

POLLUTANT

1980-1999

1990-1999

Carbon
Monoxide (CO)

57

36

Lead
(Pb)

94

60

Nitrogen
Dioxide (NO2)

25

10

Ozone
(O3)[2]

20

4

Particulate
Matter (PM10)

[3]

18

Sulfur
Dioxide (SO2)

50

36

[1]
National Air Quality and Emissions Trends Report, 1999, EPA OAQPS, Research
Triangle Park, NC, March 2001. http://www.epa.gov/airtrends/aqtrnd99/
[2] This ozone concentration is based on the 1-hour ozone NAAQS. In 1997,
EPA promulgated a new 8-hour ozone National Ambient Air Quality Standard.
However, due to legal challenges, this 8-hour standard has not yet been
implemented.
[3] Concentration measurements of PM10 for 1980 are not available.

Since 1970, population has increased 38 percent; the number of people employed
has increased 68 percent; the Gross Domestic Product has increased 147 percent;
the number of drivers has increased 68 percent; and total vehicle miles
traveled (VMT) per year have increased 142 percent. Despite these challenges,
national on-road motor vehicle emissions have declined 77 percent.

Increasingly tight EPA engine and fuel standards for both cars and trucks have been instrumental in decreasing emissions, and will continue to do so. Emissions reductions have also been the focus of other programs, such as the Congestion Mitigation and Air Quality Improvement Program, which authorized over $8 billion in TEA-21 for
transportation projects aimed at reducing
emissions.

Transit vehicles account for a very small percentage of total vehicle emissions,
less than one percent of the total. Transit operators, however, are still
making strides in improving emissions from transit vehicles through the
introduction of clean-burning, more fuel-efficient buses. Since 1992,
the share of alternative fuel buses in the transit fleet increased from
1.2 percent in 1992 to 7.5 percent in 2000. Alternative fuel transit buses
currently operate in 39 States.

Transit use also contributes to the reduction in air emissions from automobile
and truck sources. Public transportation produces about 90 percent less
volatile organic compounds, more than 95 percent less carbon monoxide, and
almost 50 percent less nitrogen oxides and carbon dioxide than private vehicles that transport the same number of people.

Reducing pollutant emissions from motor vehicles has been the major factor to this trend in cleaner air, while enhancing the community and social benefits of transportation. Technological
innovations, cleaner fuels, and targeted highway and transit programs have reduced emissions
significantly over the past 30 years, and this trend is projected to continue well into the future.